Sister Sister actress Tamera Mowry-Housley and her husband Adam Housley are mourning the loss of their 18-year-old niece Alaina Housley, who was among 12 people killed and at least a dozen more injured when a gunman opened fire at Borderline Bar and Grill in Thousand Oaks, California, on Wednesday night.

The gunman, identified by authorities as former Marine Ian David Long, was also killed.

In a statement to People, The Real host and the former Fox News correspondent confirmed the tragedy.

"Our hearts are broken. We just learned that our niece Alaina was one of the victims of last night's shooting at Borderline bar in Thousand Oaks. Alaina was an incredible young woman with so much life ahead of her and we are devastated that her life was cut short in this manner. We thank everyone for your prayers and ask for privacy at this time."

Alaina had been at the bar with a group of friends. The venue was reportedly packed with patrons.

After the shooting, Mowry had taken to social media to search for information about her niece's whereabouts. She first responded to a tweet from her niece's suitemate, who said she was still missing after the shooting.

Tamera Mowry-Housley and Adam Housley. (Instagram)

"Ashley this is her aunt Tamera Mowry Housley. Can you please DM me your information?" the actress asked.

The suitemate replied saying she had already been in contact with Mowry's husband. "Unfortunately there's nothing new to report at the moment," she said.

After a Twitter user offered her prayers, Mowry responded saying, "We haven't found her yet. It's been 7 hrs since the shooting."

Housley wrote, "Staying positive and praying and hoping and wishing there was more I could do."

Borderline Bar and Grill, a popular country venue, was hosting its weekly college night when the attack occurred on Wednesday. Ventura County Sheriff Geoff Dean said an investigation is ongoing, and it is unclear what motivated the attack.

This is the second mass shooting in the US in less than two weeks. On Oct. 27, a gunman killed 11 people at a synagogue in Pittsburgh, Pennsylvania.